In the story "The Minister's Veil" By Nathaniel Hawthorne, what is the symbol of the black veil that Parson Hooper wears?

In a society
based on the holy pursuit of perfect and election by God, Mr. Hooper dons a veil that provokes a
wide range of reactions from his parishioners. The reader never knows the specific reason why he
wears this, but we come to understand...